Known processes for applying corrosion resistant protective coatings on aluminum substrates are typically sequential in nature and utilize a chemical or electrochemical surface treatment followed by the application of an organic primer. The aluminum substrate or component is first anodized, then sealed through hydration and subsequently the sealed anodic coating is coated, typically with an organic primer.
The multiple separate and distinct process steps of the above-noted coating operation result in a build-up of layers which creates dimensional problems due to the film thicknesses of the anodic coating and the primer. This build-up of layers results in an ultimate coating having a durability which is critically dependent on the degree of chemical/mechanical bonding between layers. Moreover, the entire operation for producing the multilayered coating requires an appreciable amount of time and labor.
In an attempt to overcome the shortcomings of the known coating processes, the inventors of the present invention disclosed in Bradley et al. U.S. Pat. No. 4,310,390, assigned to the assignee of the present application, a protective coating process which reduces the number of process steps required to form a protective coating. The reduction of process steps is achieved by introducing a water-borne, water soluble acrylic resin into the sealing step of an otherwise conventional anodizing sequence to thereby simultaneously seal and impregnate the anodic coating. Subsequent to the sealing step, however, the resultant coating is cured at elevated temperatures up to 500.degree. F. The requirement of a heating step is not only costly in terms of production time and energy, but requires the maintenance of a precisely controlled temperature/time range which is difficult to achieve.